Reality, it is said, exists to diminish movie stars. When viewed on the sidewalk or under ordinary lights, stars and starlets are smaller then we need them to be, their cheekbones lower, their luminosity replaced with a dim pallor. Onscreen, they are Marlene Dietrich; in person, they're the girl at your local bakery who tells you she's out of walnut bread.

This is not the case with Rachel Weisz.

Sitting poolside in the impossibly bright patio of the Sunset Marquis in Beverly Hills, the 31-year-old actress, with her onyx eyes and porcelain skin, seems otherworldly, an apparition. "I am so uninterested in style I cannot tell you," she smiles, though it's hard to believe her. She looks a triumph of low-key L.A., in jeans and a little cropped sweater, her inky-black hair scraped back into a tight bun. As cinema's resident sex-kitten brainiac -- she's one of the few ingenues with a degree from Cambridge -- Weisz brings an enigmatic air to everything she does, whether it's a well-heeled British indie or a Hollywood spectacle. "As a person, she is kind of unknowable," explains Neil LaBute, who directed her in his Off Broadway play The Shape of Things as well as the film version, which comes out this January. "Probably the best actors are that way. They maintain a sense of mystery about themselves. She is open when you talk to her, so there is never a sense of physical hiding or standoffishness. It is almost that she has this defiant sense about her: You will never know everything about me. I will always be unreachable."

Unreachable, yes, but not inaccessible, at least to us. Weisz, a lifelong Londoner, will shortly be moving to New York. The impetus for the relocation is her boyfriend, the nihilistic Brooklyn-born director of Requiem for a Dream, Darren Aronofsky -- "We're very happy" is all she'll say -- but she's been dreaming about this move since she was a teenager. "What I am most looking forward to about New York is that you don't have to do anything," says Weisz, who first visited when she was 21. "Everything comes to you. I'm a people-watcher. It's my favorite thing. New York is the capital of people-watching."

Weisz is less comfortable with being the one who is watched. "I think people's fascination with celebrities is . . . Well, I just don't get it," she says, fumbling her words. "I don't know. I mean, who cares?" There's good reason for her discomfort. Like most single British actresses with a modicum of fame, Weisz has already suffered at the hands of the British tabloids. In 1998, her mother found out about her relationship with British television actor Neil Morrissey, star of Men Behaving Badly -- who was engaged to someone else at the time -- only after she saw their faces plastered on the front page of the Daily Mail. After that, Weisz spent time with Road to Perdition director and current Kate Winslet paramour Sam Mendes. "I have found that celebrity is something you can court or you can not court," she says. "I choose not to court it."

For all of her Cambridge education, it was the rather brainless actioner The Mummy that made Weisz -- playing a hormonally charged 12-year-old boy's fantasy of a British librarian -- famous in this country. The Mummy begat The Mummy Returns, which in turn begat a salary hike that puts her among the highest-paid British actresses and has made her "more financially secure than I ever imagined being."

"It just seems like a surreal joke that you get to dress up as somebody else and then they fly you to these incredible locations and in the end you get paid for it," she says, tensing a bit. "It's horribly naïve, I know, but I like to keep it pure and pretend there is no money involved."

Of course, she's not that naïve. Since her film debut at 24 as a topless poolside aristocrat in Bernardo Bertolucci's Stealing Beauty, Rachel Weisz (it's pronounced vice) has never shied away from trading on two of her best assets: her uncommon beauty and her raw sexuality. Her current slate of films is no different: The Shape of Things has her as a borderline-psychotic art student who physically and emotionally manipulates the weak-willed men around her, and in Confidence, a sun-soaked film noir slated for the spring, she plays a lusty pickpocket opposite Ed Burns's seasoned grifter.

Weisz was born in London, where her Hungarian-born father was an inventor -- he came up with a pioneering artificial respirator -- and her mother a Viennese psychotherapist. Being the daughter of a strict Freudian gave her a unique perspective on New Yorkers' favorite pastime. "At a young age, I saw that there was a lot of humor to be had with shrinks," she says, smiling. "Hence Woody Allen. I mean, so much of it is like, you lose your keys and then are told that in truth you did not want to come home at all. Frankly, it makes me want to pull my hair out. Shrinks give you a sense that because they're in charge of the subconscious, they know what's really going on and no one else does."

Her parents split when she was 15. "I was a terrible loner as a teenager," she says. "I hung out by myself and read Sylvia Plath." While her father forbade her to act as a teenager, fearing that it would doom her as an academic, he inexplicably allowed her to model. This year, after more than a decade and a half away from it, Weisz returned to modeling, following the lead of Julianne Moore and Halle Berry and signing as a Revlon spokesperson. "Spokesperson?" she says, raising an eyebrow. "I don't say much. I just look a certain way and they take my picture."

Weisz supplements her own casual style with occasional bouts of dressing up: "I love Gucci. That has become a rather recent obsession. I mean, until recently I dressed in thrift clothes. The only clothes I collected were Ossie Clark. I would buy his stuff at this great secondhand thrift market in Cambridge. He designed Mick Jagger's jumpsuits . . . very bohemian vogue."

At Cambridge, Weisz majored in English and co-founded an avant-garde theater company, Talking Tongues. Indeed, for all her film success, she considers her greatest professional accomplishment to have been when, in 1999, she combined her passion for southern gothic and her love of theater by treading the boards as one of Tennessee Williams's doomed heroines. "I am probably most proud of the work I did in a West End production of Suddenly Last Summer," she says, though as with many actors, her life in the theater left her with a healthy case of self-loathing -- "I look at my performances in early films and most of it is crap" -- and a filthy nicotine habit. "I gave up July 1 last year," she says. "It was the single hardest thing I have ever done. I did it with a combination of yoga and sheer will . . . a lot of will."

Quitting smoking was some forward thinking on Weisz's part, considering that her next great challenge requires her to leave home for the first time and lay roots in the land of $8 Marlboros. "I've spent time in L.A., but I've never packed up my home and brought it somewhere," she says. "This will be a big step for me. New York is the one place I've been that actually looks as good as it does in movies."

And if things don't work out here, then Weisz will always have London. "My family is there, and I will always keep my flat," she says. "I suppose it is some form of psychological safety net, but at the same time, I can't say that I am frightened of falling."